FR3045405A1 - MOBILE BED REACTOR WITH LOW RADIAL FLOW CAPACITY COMPRISING MULTIPLE PARTS CONNECTED BY FLANGES - Google Patents

Abstract

The present invention describes a mobile bed reactor of catalyst and radial flow of the so-called radial moving bed reactor, consisting of 3 zones called upper hemispherical body (III), lateral zone (II) and lower hemispherical body (I), the 3 zones being connected together by means of flanges.

Description

MOBILE BED REACTOR WITH LOW RADIAL FLOW CAPACITY OF THE LOAD CONSISTS OF SEVERAL RELATED PARTS

BY BRIDGES

BACKGROUND OF THE INVENTION

A number of refining and petrochemical processes rely on reactors known as radial reactors. Among these methods, the following may be mentioned without being limited: catalytic reforming of gasolines, oligocracking of olefinic cuts, dehydration of alcohols (ethanol, propanol, isobutanol), skeletal isomerization of olefins, metathesis for the production of propylene, dehydrogenation of paraffins.

In a radial bed reactor the catalytic bed has the shape of a vertical cylindrical ring limited on the inner side by an inner grid, called gate of the central collector, retaining the catalyst, and on the outer side, or by another grid of the same type that the inner grid and called external grid, or by a device consisting of an assembly of grid elements in the form of shells (called "scallops" in the English terminology).

This reactor geometry is the one that is used mainly in the industry, but it requires a minimum external rack space / central collector so that, during maintenance operations of the reactors, the operators can pass between the grids in order to inspect them and to clean them (broken catalysts deposited between the grids).

The current design rules recommend two criteria that may prove to be contradictory for radial beds: a minimum catalytic bed thickness of approximately 400 mm so as to achieve the minimum limit for the maintenance of the grids, and a minimum pressure drop to the crossing of the bed between 20 and 80 mbar (mbar is the abbreviation of millibar or 10'3 bar) inside the radial bed in order to maintain a good distribution of the gas in the catalytic bed, without blocking of the flow of the catalyst.

However, for low reactor capacity, maintaining a sufficient pressure drop for the proper distribution of the load over the entire height of the reactor involves shortening the bed (increase of the superficial velocities).

Moreover, below a certain critical capacity, this shortening is limited by the minimum thickness of 400 mm, not allowing to maintain the pressure drop criterion. There is therefore a need for a technological solution that makes it possible to release at least one of the two criteria, possibly both, in order to maintain the possibility of dimensioning radial beds, in particular mobile beds, for low capacities.

SUMMARY DESCRIPTION OF THE FIGURES

FIG. 1 represents a schematic view of a radial bed reactor according to the invention.

EXAMINATION OF THE PRIOR ART

In the prior art relating to radial bed reactors, mention may be made of US Pat. No. 6,221,320, which provides a fairly complete summary of conventional technologies. According to the state of the art, the catalytic bed in a moving radial bed reactor is delimited by two grids, an internal grid and an external grid. More specifically, one generally distinguishes: • An internal grid which delimits the central collector of the gaseous effluents, • An external grid which delimits the volume of supply of the charge in the gaseous state.

The process fluid arrives through the external volume defined between the shell and the outer gate. It then passes through the catalytic bed substantially horizontally and perpendicular to the flow of catalyst which is gravitational, that is to say substantially vertical from top to bottom and obtained under the sole effect of the weight of the catalyst bed.

The process fluid in radial flow, and the gravitational flow catalyst are separated by the internal grid which generally has a cylindrical shape with the same substantially vertical axis as the external grid.

The cylinder, or more generally the substantially cylindrical shape, defined by the internal grid, serves as a central collector to evacuate the gaseous effluents from the reaction zone between the outer gate and the inner gate and therefore of substantially annular shape.

The constraints related to mobile radial bed technology are multiple. In particular, the gas velocities at the crossing of the catalytic bed are limited in order to: • avoid cavitation at the entrance of the bed, • avoid the blockage of the catalyst at its exit against the internal grid, • reduce the pressure losses depending on the speed and the thickness of the bed.

For reasons of homogeneous distribution over the entire height of the catalytic bed, a perforated tube designed to create the pressure drop can be added to the central collector.

Finally, for construction reasons, it is often necessary to leave sufficient space between the internal grid and the external grid. Finally, when all the constraints for this reactor configuration are combined, the minimum volume of catalyst that can be enclosed in the annular zone can not fall below a certain minimum value.

In general, according to the prior art, the maximum PPHs accessible in the mobile radial beds are of the order of 20 h -1, whereas the reactor according to the present invention makes it possible to reach PPHs greater than 50 h -1. or even greater than 100 h'1.

SUMMARY DESCRIPTION OF THE INVENTION

The present invention describes a small bed reactor with moving bed and radial flow of the load.

By moving bed is meant a bed that flows gravitarily, often at a slow speed, of the order of one meter per hour, and in a substantially vertical direction.

This type of flow is found in many reactors, in particular the reactors used for the catalytic reforming of gasolines which requires a complex regeneration step of the catalyst.

Finally, small size means reactors whose catalyst bed thickness, that is to say the radial dimension between the outer gate and the central collector, is between 100 and 400 mm.

More specifically, the reactor according to the present invention can be defined as a moving bed reactor, with radial flow of the feedstock and gravity flow of the catalyst consisting of 3 sets called upper hemisphere body (III), lateral zone (II). and lower hemisphere body (I).

Overall, this reactor has a cylindrical symmetry around its substantially vertical central axis.

The upper hemispherical body (III) is provided with an intake duct (6) of the feedstock and catalyst introduction legs (7) communicating with conical elements (9) which give access to the annular zone (11). ) located between the central collector (4) and the external grid (3). The conical elements (9) form a volume of conical shape and of the same cylindrical symmetry as the reactor itself.

The central collector (4) is equipped on its outer face with a grid of the same type as the outer grid (3). It is closed at its upper end by a solid plate (5).

The external grid (3) is placed parallel to the side wall (II) of the reactor at a distance from the latter, and the central collector (4) extends substantially along the longitudinal axis of symmetry of the reactor over the entire height of the annular zone (11a) and extends over a certain height inside the lower hemispherical body (I).

A certain space (not shown in Figure 1) is arranged between the side wall (II) and the outer gate (3).

The outer grid (3) rests on a support ring (2) which is preferably fixed on the wall of the lower hemispherical body (I).

In some cases this external grid (3) may consist of an assembly of shell-shaped grid elements extending longitudinally over the entire height of the annular zone (11a).

The annular zone (11a) extends between the external grid (3) and the central collector (4). This annular zone (11a) corresponds to the catalytic zone over a radial distance of between 100 and 400 mm.

The height of said annular zone (11a) generally corresponds to the height of the lateral zone (II), but may, in some cases, overflow into the lower hemispherical (I) and upper (III) bodies.

The load passes through the annular zone (11a) radially, that is to say substantially horizontally, from the outer gate (3) to the central collector (4), and the catalyst flows vertically from high to bottom of said area.

It remains within the scope of the invention if the load passes through the radial bed in the opposite direction, that is to say from the center of the reactor to the periphery.

In this case the central collector (4) acts as a distribution grid, and the outer gate (3) acts as a peripheral collector effluents.

It is also within the scope of the invention if the load is provided by the pipe (1), then discharged through the pipe (6).

The lower hemispherical body (I) carries the exhaust legs (8) of the catalyst and the discharge pipe (1) of the reaction effluents, the reactor being characterized in that the upper hemispherical body (III) is connected by flanges. B3, B4 to the lateral zone (II), and in that the lower hemispherical body (I) is connected by the flanges B1 and B2 to said lateral zone (II).

The flanges B1 to B4, the size of which is well known to those skilled in the art, are not described.

The present invention also relates to any method using the moving bed reactor previously described.

In the context of the catalytic reforming process for gasolines, cited here by way of non-limiting example, the reactor according to the invention is generally placed at the head of the series of reactors constituting the reforming unit, in which process: charge enters the reactor by means of the inlet pipe (6) located in the upper part (III) of the reactor and enters the annular zone (11a) situated inside the lateral body (II) while passing through the external grid (3), the load passes through the catalytic bed contained in the annular zone (11a) in a substantially radial manner, and the effluents resulting from the catalytic reaction are collected in the central collector (4) and then are discharged from said reactor by the outlet pipe (1) implanted on the lower hemispherical body (I), • the catalyst is admitted into the annular zone (11a) by one or more legs (7) which communicate with said annular zone With the aid of conical elements (9), the catalyst flows gravitarily into the annular zone (11a) and is then discharged from the reactor via discharge legs (8) located in the lower hemispherical body (I).

Finally, the present invention also relates to a method for constructing the reactor according to the invention, in which: a) the lower body (I) of exhaust legs (8) is equipped for the evacuation of the catalyst, and effluent outlet pipe (1) which is provided at its upper end with a means allowing its attachment to the central collector (4), b) the central collector (4) is arranged in the lateral body (II), and said central collector (4) is attached to the effluent discharge pipe (1), c) the central collector (4) is closed at its upper end by a solid plate (5), and (d) the lower body (I) is fixed. ) to the lateral body (II) by an assembly of flanges (B1) and (B2) carried by the lateral body (II) and the lower body (I), e) an external grid (3) or grid elements is fixed external to a support ring (2) arranged in the assembly formed by the lateral body (II) and the lower body (I), f) the upper body (III) is fixed to the lateral body (II) by means of an assembly of flanges (B3) and (B4), said upper body (III) being previously equipped with a charge introduction pipe (6) and descent legs (7) allowing the catalyst to enter the reactor.

Thanks to the flange mounting according to the invention, it is very easy to remove the internal (external grid (3) or grid elements and central collector (4)), and thus inspect and / or change and / or clean.

The time required for these operations is therefore minimized compared to current reactor configurations, which do not allow maintenance operations easily for low capacity.

In the case of small size reactors with a catalytic bed thickness of less than 400 mm, the solution according to the invention of the division of the 3-body reactors (I), (II) and (III), and of the flange assembly of these bodies is the most efficient vis-à-vis the maintenance aspect.

DETAILED DESCRIPTION OF THE INVENTION

The following description is made with reference to FIG.

The reactor comprises three parts: - a lower body (I), - a lateral body (II) also called reactor body, - an upper body (III).

We speak of annular zone (IIa) to designate the catalytic zone contained in the lateral body (II).

The lower body (I), generally of hemispherical shape, also called lower hemispherical body, comprises an effluent outlet pipe (1) located in said lower body and is closed near the ring in its upper part by the ring. support (2).

This lower body (I) is provided with a flange (B1) welded along the substantially circular perimeter of said lower zone (I). The support ring (2) is limited in its radial dimension to allow movement of the catalyst from the annular body (11a) to the discharge legs (8) implanted on the lower hemispherical body (I). The support ring (2) is not always strictly at the flange (B1, B2), but may be welded to the wall of the lower hemispherical body (I) or the lateral body (II).

It can in some cases be found, at least partly, in the lateral body (II).

The catalyst is introduced into the upper hemispherical body (III) by introduction legs (7) which are themselves in communication with the annular zone (11a) by means of the conical portions (9).

The catalyst flows gravitarily into the annular zone (11a), then is taken up by the evacuation legs (8) whose upper end is in the lower hemispherical body (I).

The external grid (3), arranged parallel to the side wall of the body (II) makes it possible to distribute the charge over the entire height of the lateral zone (11a) so that it is brought into contact with the whole of the catalyst contained in the annular zone (11a). The charge passes through the annular catalytic zone (11a) in a substantially radial manner, and the effluents are recovered in the central collector (4).

The upper part of the catalytic zone (11a) is closed by the conical elements (9) which are generally bolted to the central collector (4) and / or to the external grid (3).

Any other connection known to those skilled in the art, to ensure the assembly of these conical elements (9), can also be used.

The upper part of the central collector (4) is closed by a solid plate (5).

The lateral body (II) is provided with a flange (B2) welded throughout the lower part of the substantially circular perimeter of said lateral zone (II), and a flange (B3) welded throughout the part. upper part of said lateral zone (II).

The solid plate (5) is not necessarily at the flange B3. In this case, links can be put in place between the flanges and the solid plate (5) to facilitate the installation of said solid plate (5).

In the case where the solid plate (5) is approximately at the same level as the flange (B3), said solid plate (5) and the conical parts (9) are connected to the wall by assembly by means of a ring external (not shown in Figure 1) ·

Spaces must be arranged at the periphery of the upper body (III) to let the gas pass to the space delimited by the wall of the lateral body (II) and the external grid (3), or the grid elements when the latter is consisting of elements (called "scallops" in English terminology).

The lateral body (II) is provided with a flange (B3) welded along the upper part of the substantially circular perimeter of said lateral zone (II).

The upper body (III) is also equipped with a flange (B4). The assembly of the flanges (B3) and (B4) is conventionally performed by bolting, or by any other means known to those skilled in the art.

The upper body (III) is provided with a feed inlet duct (6), and catalyst introduction legs (7).

These legs (7) have their lower end communicating with the conical elements (9) for feeding the entire annular zone (11a), so-called predistribution function of the catalyst.

A leg (7) is generally inserted in the corresponding conical part (9) via a sliding connection, this connection to be sealed to the catalyst.

Given the solid plate (5) closing the gaps left between the conical elements (9), the charge introduced into the upper hemispherical body (III) through the pipe (6) passes through the outer grid (3) and then passes through the bed contained in the annular zone (11a) substantially radially after passing through the outer grid (3).

The reaction effluents are collected in the central collector (4) and pass into the lower hemispherical body (I), from where they are evacuated via the pipe (1).

The connection between the central collector (4) and the outlet pipe (1) is generally made by a flange, but other modes of connection are possible while remaining perfectly within the scope of the invention.

A perforated tube (not shown in Figure 1) is often attached to the central collector (4) in order to improve the gas distribution over the entire height of the reactor generating an additional pressure drop.

The outer grid (3) can optionally be replaced by an array of shell elements forming a continuous assembly (elements called "scallops" in the English terminology).

The present invention also relates to a method of mounting the reactor according to the invention which can be described as follows: a) the lower body (I) of exhaust legs (8) is equipped for the evacuation of the catalyst, and an effluent outlet pipe (1) which is provided at its upper end with a means for attaching it to the central collector (4), b) the central collector (4) is arranged in the lateral zone (11). ), and attaching said central collector (4) to the effluent discharge pipe (1), c) closing said central collector (4) at its upper end by a solid plate (5), d) fixing the lower body (I) to the lateral body (II) by an assembly of flanges (B1) and (B2) carried by said lateral body (II) and said lower body (I), e) an external grid (3) is fixed or outer gate members to a support ring (2) disposed in the assembly formed by the lateral body (II) and the lower body (I), f) the upper body (III) is fixed to the lateral body (II) by means of an assembly of flanges (B3) and (B4), said upper body (III ) being previously equipped with a pipe (6) for introducing the load and descent legs (7) allowing the arrival of the catalyst in the reactor.

EXAMPLE ACCORDING TO THE INVENTION The objective is to treat a load of 20 t / h, with a density of 5 kg.m-3 and a viscosity of 0.02 mPa.s, through an enclosure comprising a mobile catalytic bed having the shape a vertical cylindrical ring limited on the inner side by an inner cylindrical grid, defining the central collector (4), and on the outer side by a cylindrical grid (3) of the same type as the inner grid. After passing through the catalytic bed, the reaction effluents are collected in the vertical cylindrical collector.

The catalyst is in the form of a grain with a diameter of 2 mm and with a void fraction between grains of 40%.

The PPH, that is to say the ratio between the mass flow rate of the feed and the weight of catalyst contained in the reactor is set at 50 h -1.

Two dimensions of the internals are proposed in Table 1, according to the prior art and according to the present invention.

The main difference between the design of the reactor according to the invention and according to the prior art lies in the constraint in terms of catalytic bed thickness (greater than 400 mm according to the prior art).

The catalyst volume of 0.6 m3 is the same in both situations.

The operating conditions are as follows:

-Reactor inlet temperature: 520 ° C

-Motor temperature in the reactor: 467 ° C -Pressure 0.7 MPa (MPa is the abbreviation of mega Pascal or 106Pa)

The load is defined by the following characteristics: initial boiling point 80 ° C, boiling point 180 ° C:

Its breakdown into chemical families is given below:

The main elements of the design are summarized in Table 1 below. Under the operating conditions of the process, it is clear that the sizing according to the prior art is not suitable, for two reasons: - a loss of pressure much too important, with multiple consequences, especially in terms of operating costs the process, - a difficult inspection of the central collector (4) due to its small diameter, - too high speeds in the radial bed, which leads to a risk of blockage of the catalytic flow.

Table 1

In Table 1, the following abbreviations are used: CC: central collector (4). GE: external grid (3). The thickness is the radial dimension between the external grid (3) and the central collector (4).

The input speed is taken at the outer gate (3).

The output speed is taken at the central collector (4). DP: pressure drop in the radial dimension of the catalytic bed from the external grid (3) to the central collector (4).

Claims (5)

1) Reactor in moving bed and radial flow of the load and gravity flow of the catalyst consisting of 3 sets called upper hemispherical body (III), side body (II) and lower hemispherical body (I), the upper hemispherical body (III) being provided with an inlet duct (6) for the feedstock and catalyst introduction legs (7) communicating with conical elements (9) which give access to: - the annular zone (11a) situated between the central collector (4) and the outer gate (3) over a radial distance of between 100 and 400 mm, said outer gate (3) being placed parallel to the reactor side wall (II) and at a distance from this last, and the central collector (4) extending substantially along the longitudinal axis of symmetry of the reactor over the entire height of said lateral zone (11a) and extending inside the hemisphere body the lower part (I) which carries the catalyst outlet legs (8) and the effluent outlet pipe (1), itself connected to the lower end of the central collector (4), the outer gate ( 3) being supported by a support ring (2), extending over the entire periphery of the lower hemispherical body (I) and fixed thereto, and the central collector (4) being closed at its upper end by a solid plate (5), said reactor being characterized in that the upper hemispherical body (III) is connected by flanges B3, B4 to the lateral body (II), and the lateral body is further connected by flanges B1, B2 to the hemispherical body lower (I). 2) Reactor according to claim 1, wherein the outer grid (3) consists of an assembly of shell-shaped grid elements extending longitudinally over the entire height of the annular zone (11a). 3) Process using the reactor according to claim 1, wherein: • the feed enters the reactor by means of the inlet pipe (6) located in the upper part of the upper hemispherical body (III) of the reactor and enters the zone annular (11a) located inside the lateral body (II) through the outer gate (3), • the load passes through the catalytic bed contained in the annular zone (11a) substantially radially, and the effluents resulting from the catalytic reaction are collected in the central collector (4), then • the effluents are discharged from said reactor through the outlet pipe (1) continuously attached to the central collector (4), • the catalyst is admitted into the annular zone (lia ) by one or more legs (7) implanted in the upper hemispherical body (III) which communicate with said annular zone by conical elements (9), the catalyst flows gravitarily into the the annular zone (11a), then is discharged from the reactor by evacuation legs (8) implanted in the lower hemispherical body (I). 4) Process according to claim 3 selected from catalytic reforming gasolines, skeletal isomerization of olefins, metathesis for the production of propylene, oligocracking, dehydration of alcohols. 5) A method of construction of the reactor according to claim 1, wherein: a) the lower body (I) is equipped with exhaust legs (8) for the removal of the catalyst, and a discharge pipe (1). ) of the reaction effluents which is provided at its upper end with a means allowing its attachment to the central collector (4), b) the central collector (4) is arranged in the lateral zone (11a), and said central collector ( 4) to the effluent discharge pipe (1), c) said central collector (4) is closed at its upper end by a solid plate (5), d) the lower body (I) is fixed to the lateral body ( II) by an assembly of flanges (B1) and (B2) carried by said lateral body (II) and said lower body (I), e) an external grid (3) or external grid elements are fixed to a ring of support (2) arranged in the assembly formed by the lateral body (II) and the lower body (I), f) the upper body (III) to the lateral body (II) by means of an assembly of flanges (B3) and (B4), said upper body (III) being previously equipped with a pipe (6) for introducing the load and descent legs (7) allowing the arrival of the catalyst in the reactor.